I shoot weddings, generally for people who cant afford a pro. However I stipulate I prefer not to do indoor photos and will do the reception but not keen on doing so. I am happy to do outdoor weddings in natural light and fill flash. I take a second photographer and so far have not had any complaints about the photos. I spend a lot of hours editing the photos. I find weddings quite stressful and would not recommend you doing an indoor wedding unless you feel very confident in your work. If you choose to do it, good luck

i have not shoot a wedding for years now and all i can sy is that it is nerve racking this is a one off shoot and it has to be right. if it is going to be all in side then you really need to know a lot about flash photography to get good results. i agree with the other posts here you need a really good flash gun you need to know the size of the venue and how that will affect the flash.
its already been said here that being a 2nd shooter maybe better thats how i learnt and my mentor then passed judgement of my efforts. there is so much to remember on a wedding shoot, its ok after you have a few under your belt, but if this is the first then it will be tough.
i dont know your skill and i hate to be negative to people but weddings are not the best thing to hone your skills on theres enough to worry about any way
best of luck anyway if you go ahead with it

My advise is that if you need to ask what you need to do, you should not agree to shoot the wedding. If you make mistakes and the photos do not turn out well, it's not like you can ask them to have another wedding to try and get better results, practicing until you get it right. You only get one shot at it, and you need to have the experience, skill level and equipment needed to insure those photos come out well (with the emphasis on the experience and skill level). Otherwise, you could contribute to bitter feelings between you guys if something goes wrong (and refer to Murphy's law when shooting weddings). ;-)

Taking photos indoors in difficult environments takes practice, especially if you're using MF lenses with a camera that has a small viewfinder without a split prism type focus screen, making it difficult to determine focus accuracy (I'm assuming that the 35-70mm you're mentioning is an older OM type lens).

That's not a great focal length if you're shooting in closer quarters with a four thirds system camera either (as it would have the same angle of view you'd have using a 70-140mm lens on a 35mm camera, which could make it difficult to back up far enough to get what you want in the frame shooting in bar/restaurant environment, depending on how large it is).

What kind of flash system are you using now? Do you have experience making changes to settings as needed in difficult indoor environments to compensate for ceiling height/color, subject colors, distance, etc. to accommodate for metering difficulties using a flash in that environment?

What kind of backup gear do you have (camera bodies, lenses, flash systems, etc.) in case something breaks or malfunctions?

Here is one 6 page article that may help you understand the difficulty and challenges involved:

Do you have any experience at all in this area, or comparable experience shooting a lot of indoor [people] subjects with your existing gear in comparable conditions?

Do you have adequate backup equipment to use when problems occur?

I'll move this thread to our General Discussion forum for more comments. I'd give more info on the exact conditions, what equipment you have available, your experience level, etc. But, if you've never shot similar subjects in similar conditions, I'd suggest bowing out gracefully and asking them to find a professional photographer with experience shooting weddings in those conditions instead.